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<script>
    // ES5 var 使用
    var a = 10;
    a = 20;
    console.log("a1:", a)
    // var a = 20;
    // console.log("a2:", a)
    // ES6 let 使用
    let b = 20;
    b = 30;
    // alert(b)
    console.log("b1:", b)
    // let b = 30
    // console.log("b2:", b)

    const c = 30;
    // c = 31;
    console.log("c1:", c)

    let str = prompt("请输入内容")
    console.log("str:", str)


</script>


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